1. Field of the Invention
The present invention relates to telephone systems and more particularly to methods and apparatus for upgrading an existing tip and ring prior art telephone system which uses a pair of copper conductors for each bidirectional connection between two distribution terminals to a system which requires only two pairs of existing copper (or other metal) conductors for carrying a plurality (such as twenty-four) bidirectional communications between the two distribution terminals. The invention also relates to such methods and apparatus for upgrading a telephone system which, after being upgraded according to the teachings of this invention, is compatible for still further and future upgrades.
2. Description of Related Art
Over the last twenty years, the demands for xe2x80x9ctelephonexe2x80x9d-type communications has increased at exponential rates. Telephone-type communications, or xe2x80x9ctelephony,xe2x80x9d is no longer simply applicable to telephone voice communications. In fact, the demands on the infrastructure and existing telephone systems from other types of telephony such as faxes, computer modems, etc. and other broadband uses now exceed voice communications in most locations.
Consequently, telephone systems in these high-density areas now use many different high speed, broadband transmission techniques, including light transmission through optical fibers. Yet, even though there are areas of communications or physical locations demanding this very high-density type of service, there are likely to be other areas or communications or physical locations immediately adjacent where the demands on telephone service has increased only slightly from the demands of twenty years ago. Therefore, methods and equipment must be provided which interface various levels of service demands.
It is therefore not unusual to require different upgrade levels of a telephone system depending upon these highly varying needs. In addition, because new and different services which require high-speed and broad-band telephone communications seem to be hitting the market every day, it is also desirable to provide methods and apparatus for upgrading a telephone system, which upgrade will also allow for continuous and much expanded upgrades of service in the future with minimal change to the existing infrastructure.
Therefore, it is an object of the invention to provide methods and apparatus to increase the number of communication channels carried by existing copper wire pairs.
It is yet another object of the present invention to provide methods and apparatus for efficient and cost effective upgrading to existing infrastructure copper wire communication pairs.
These and other objects can be achieved by the present invention which provides bidirectional telephone delivery circuitry and methods for supporting a multiplicity of telephone subscriber lines at a downstream distribution terminal using only two of a multiplicity of pre-existing transmission line pairs connected between an upstream distribution terminal and the downstream distribution terminal. The methods and apparatus comprise an upstream distribution terminal which may receive and transmit PCM telephone signals to and from one location. These PCM signals are transmitted to conversion circuitry which includes an HDSL driver and receiving circuit for receiving HDSL TDM signals from a downstream terminal and for transmitting corresponding HDSL TDM signals to the downstream terminal on a pair of transmission line pairs. A pair of HDSL isolation transformers are included and, according to one embodiment, each of the pair has an upstream side coil connected to the HDSL driver and receiver circuit and each also has a downstream side coil connected to one of two conductor pairs such as a pair of copper tip and ring conductors typically used for existing voice telephone service. Each of the downstream coils of the two transformers also includes a center tap. There is included power circuitry for providing a source of regulated and current limited DC power which has a power output terminal and a return terminal. The power output terminal is connected to the center tap of one of the pair of isolation transformers, and the power return terminal is connected to the center tap of the other one of the pair of isolation transformers. Two transmission line pairs are chosen from the existing, twenty-four conductor transmission line pairs typically used for tip and ring voice telephone service. The two transmission line pairs will typically be selected from the existing multiplicity of infrastructure telephone transmission lines located between the upstream distribution terminal and the downstream distribution terminal. As mentioned above, one of the transmission line pairs is connected to each side of the downstream coil of one of the isolation transformers and the other one of the transmission line pairs is connected to each side of the downstream coil of the other one of the transmission line pairs. The existing infrastructure at the downstream distribution terminal will typically include a multiplicity of telephone subscriber lines connected between a plurality of user locations such as homes or businesses and the downstream distribution terminal. Thus, the downstream distribution terminal is located between the two conductor transmission line pairs and the selected multiplicity of telephone subscriber lines. The downstream distribution terminal will also include a pair of isolation transformers and an HDSL TDM driver and receiver circuit substantially similar to that in the upstream distribution terminal which connects with the HDSL TDM driver and receiver circuit located in the upstream distribution terminal through the two transmission line pairs. The DC power distribution circuit provides a DC power source in the downstream distribution terminal and includes at least a pair of output terminals and an input power terminal connected to the center tap of the isolation transformer connected across one of the transmission line pairs and an input power return terminal connected to the center tap of the other isolation transformer connected across the other one of the transmission pairs so as to receive the source of regulated and current limited DC power from the upstream distribution terminal.
The power circuitry located in the upstream distribution terminal provides the regulated and current limited DC power to the downstream distribution terminal on two transmission line pairs which also carry HDSL TDM bidirectional telephone signals. The HDSL TDM circuitry comprises a pair of HSDL isolation transformers and the downstream coil of the isolation transformers each include center taps, each one connected to the power output terminal and the other center top connected to the power return terminal.